If you use the Tormach Tool System in conjunction with your power drawbar, it appears that you can use a MT3 collet to hold the interchangeable tools. According to the website:
Miscellaneous TTS Tools
you can get the Part Number 30251 - TTS-MT3 Adapter collet which would release the tools when the drawbar was engaged. I haven't used one myself (my SX3 is R8), but I doubt Tormach would sell a collet as the heart of the system that wouldn't easily release the toolholders. $20 (maybe more in Australia) would be cheaper than replacing the spindle; and might be worth giving a shot to see how well it worked.
You can see my drawbar on my SX3 briefly in action on this Youtube video:
http://www.youtube.com/watch?v=_2w8cYXt5_o]Tormach TTS-Style Toolholders on the SX3 Part 1 - YouTube
as well as using the SX3 itself to make TTS-style toolholders. I have since upgraded my setup from one that simply presses down on the drawbar (and thus stresses the spindle bearings) to a "squeeze" system that forces the drawbar down while supporting the spindle. A video for that is in the works, but it has taken second place to my attempts to get CNC spindle control for the SX3, which is taking up all of my time at the moment.